Abstract: Objective To explore the reversal effect and mechanism of low-frequency ultrasound combined with microbubbles (LFUSMB) on the multidrug resistance of breast cancer resistant strains MCF-7/Adriamycin (ADR) through the phosphatidylinositol 3-kinase (PI3K)/protein kinase B (AKT) pathway. Methods The CCK-8 method was used to screen the action time of LFUSMB and determine the half inhibitory concentration (IC50) of ADR on MCF-7/ADR cells. The MCF-7/ADR cells were divided into: control group (normally cultured with MCF cell culture medium), ADR group (used MCF cell culture medium with ADR, final concentration 20 mg/L), LFUSMB+ADR group (cultured with MCF cell culture medium with ADR, final concentration 20 mg/L and treated with LFUSMB for 30 s) and LFUSMB+ADR+740 YP (PI3K/AKT pathway activator) group (MCF cell culture medium added with ADR, final concentration 20 mg/L and 740 YP, final concentration 50 mg/L, and were cultured and treated with LFUSMB for 30 s). Annexin V-FIFC/PI method was used to detect the apoptosis rate of MCF-7/ADR cells. Western blot assay was used to detect the expression of glycoprotein (P-gp), multidrug resistance protein (MRP) 2, breast cancer resistance protein (BCRP/ABCG2), PI3K, AKT, p-PI3K, p-AKT and MRP1 proteins. Results The LFUSMB intervention for 30 s was used for the follow-up study. The IC50 of ADR to MCF/ ADR cells was lower in the LFUSMB 30 s group than that of the non-ultrasound group, and the relative drug resistance reversal ratio was approximately 8.20 times. The apoptosis rate of MCF-7/ADR cells was significantly higher in the ADR group than that in the control group (P＜0.05). There were no significantly differences in the protein levels of MRP1, MRP2, P-gp, BCRP, p-PI3K/PI3K and p-AKT/AKT between the two groups. The apoptosis rate of MCF-7/ADR cells was higher in the LFUSMB+ADR group than that in the ADR group (P＜0.05), and the protein levels of MRP1, MRP2, P-gp, BCRP, p PI3K/PI3K and p-AKT/AKT were significantly lower than those in the ADR group (P＜0.05). Compared with the LFUSMB+ ADR group, the cell apoptosis rate was significantly decreased in the LFUSMB+ADR+740 YP group (P＜0.05), and the protein levels of MRP1, MRP2, P-gp and BCRP/ABCG2 were significantly increased (P＜0.05). Conclusion LFUSMB can reverse the drug resistance of breast cancer MCF-7/ADR cells by inhibiting the activation of PI3K/AKT pathway and down regulating the expression of ATP-binding cassette (ABC) family proteins.

Key words: breast neoplasms, apoptosis, ultrasonic therapy, MCF-7 cells, P-glycoprotein, adriamycin, low-frequency ultrasound/microbubble, PI3K/AKT pathway